1. Field of the Invention
The present invention relates to a gain compensation circuit, and more particularly to a gain compensation circuit applied to an outdoor microwave transceiver.
2. Description of the Related Art
Generally, the gain of a normal transceiver will decrease at high temperatures (about 40° C. to 60° C.), but increase at low temperatures (below about 20° C.). Therefore, for some outdoor satellite transceivers which usually operate in suboptimal environmental conditions, unless gain compensation for varying temperature situations is considered, the gain of the transceiver will vary with the environmental temperature, causing signal distortion and deteriorating communication quality. Therefore, for such transceivers, it is common practice to design a compensation circuit which is able to suppress the gain of the transceiver at low temperatures but enhance the gain of the transceiver at high temperatures.
For the gain compensation of an outdoor transceiver, a passive attenuator cooperating with a thermistor is commonly used to act as a gain compensation mechanism of the transceiver. However, such structure will degrade the quality of noise figure of the transceiver due to gain attenuation. Another known method is to use the feature of a particular gain relating to temperature of an active amplifier to achieve the effect of gain compensation. However, this method has the drawback of a high material cost.